The present invention pertains to a system for and method of treating articles. Further, the present invention pertains to a lamp system usable in an article treating system and method. More particularly, the present invention pertains to controlling the cooling of an air-cooled lamp, such as an ultraviolet lamp, so as to optimize operation of the lamp.
Lamps, and in particular ultraviolet lamps such as electrodeless ultraviolet lamps, are utilized in various manufacturing operations. By way of example, many materials are cured by exposure to ultraviolet radiation from electrodeless ultraviolet curing lamps. Such electrodeless lamps are energized by, for example, a magnetron which receives power from a power supply and generates microwaves that energize the electrodeless ultraviolet lamp. Such an ultraviolet lamp must not be allowed to become overheated, or the life of the lamp will be significantly shortened. In use in commercial operations, such as curing of materials that have been applied on products being manufactured, the lamps might be operated at a high power level. To avoid overheating of the lamps, cooling air is blown onto the lamps from a blower. If the lamps are continuously operated at their intended full-power level, cooling air at a high pressure is required. This results in a high energy requirement for the blower providing the cooling air.
To avoid this, it is known to operate the lamps at a somewhat lower power level. While this enables adequate cooling to be provided with air at a lower pressure, it also reduces the efficiency of the curing process since the lamps emit less radiation at the lower power level. It is also known to operate the lamps with a duty cycle of, for example, four seconds on and one second off. High efficiency ultraviolet lamps use multiple element emitter type fills, such as mercury and iron halides. In normal operation such lamps might have a temperature in the range of from about 750xc2x0 C. to about 950xc2x0 C., and these fills are in a gaseous state. If the ultraviolet lamp is shut off for any significant time, the fills may condense. In addition, if the lamp is turned off, then the ionized plasma extinguishes and the mercury vapor must be allowed to cool for a period of time, generally between fifteen seconds and two minutes, before the lamp can again be powered. This can significantly delay the process in which the lamps being used. Additional problems which can result from such overcooling include unstable and erratic ultraviolet output levels, especially at 60% and lower power levels, delays in ultraviolet output response of three seconds or more when going from lower power to high power, spectral changes, resulting in shifting of the ultraviolet band, which can have a negative impact in some ultraviolet curing applications, bulb fill condensation, resulting in unwanted chemical reactions of some bulb fill additives with the ultraviolet lamp bulb, thereby reducing the bulb life, and excessive noisy and unnecessary cooling at power levels less than 100%. As a consequence, rather than turning such lamps off during their duty cycle, the lamps are usually powered at a low level, for example being provided with 2% to 50% of their intended full power.
If the ultraviolet lamp is provided with cooling air a constant pressure, then during the high power portions of the duty cycle, the lamp temperature increases, while during the low power portions of the duty cycle, the temperature of the lamp decreases. It is necessary to maintain the lamp temperature within an operating range of about 700xc2x0 C. to about 1000xc2x0 C., preferably 750xc2x0 C. to 950xc2x0 C., since temperatures lower than that range can result in the lamp fills condensing, causing damage to the lamp, while temperatures in excess of the range can shorten the lamp life. To accommodate this, it is known to adjust the air pressure in proportion to the power provided to the ultraviolet lamp. See, for example, U.S. Pat. No. 4,032,817. However, in fact the cooling requirements are not proportional to the power provided to the ultraviolet lamp. Consequently, such systems can overcool the ultraviolet lamps.
The present invention is a system for and method of controlling the cooling in a lamp system, as well as a system for and method of treating articles with a lamp system. In accordance with the present invention, an air-cooled lamp such as an electrodeless ultraviolet lamp, is provided with power, while an air blower blows air onto the air-cooled lamp to cool the lamp, and a blower driver is responsive to the power level of the power being provided to the air-cooled lamp to drive the air blower at a speed blowing air onto the air-cooled lamp with an air pressure having a non-linear relationship with the power level when the power level is expressed as a percentage of the lamps intended full-power level. Preferably, the relationship is substantially exponential or is substantially defined by Ap=(Pxe2x88x92Po)2, where Ap is the air pressure, P is the power level of the power being provided to the air-cooled lamp as a percentage of the full-power level, and Po is a power level as a percentage of the full-power level that when provided to the air-cooled lamp requires no air to be blown by the air blower onto the air-cooled lamp. Preferably, also, the cooling level is minimized as much as possible at all power levels, while not overheating the air-cooled lamp. Further, the present invention is a machine-readable medium having stored thereon at least one sequence of instructions that, when executed, cause a machine to cool an air-cooled lamp.